ATV Demod: implemented BFU with PLL for single sideband modes

CMakeLists.txt

@@ -126,6 +126,7 @@ set(sdrbase_SOURCES
     sdrbase/dsp/basebandsamplesink.cpp
     sdrbase/dsp/basebandsamplesource.cpp
     sdrbase/dsp/nullsink.cpp
+    sdrbase/dsp/recursivefilters.cpp
     sdrbase/dsp/spectrumscopecombovis.cpp
     sdrbase/dsp/spectrumscopengcombovis.cpp
     sdrbase/dsp/scopevis.cpp
@@ -235,6 +236,7 @@ set(sdrbase_HEADERS
     sdrbase/dsp/phasediscri.h
     sdrbase/dsp/phaselock.h
     sdrbase/dsp/pidcontroller.h
+    sdrbase/dsp/recursivefilters.h
     sdrbase/dsp/samplesinkfifo.h
     sdrbase/dsp/samplesourcefifo.h
     sdrbase/dsp/samplesinkfifodoublebuffered.h

plugins/channelrx/demodatv/atvdemod.cpp

@@ -51,6 +51,8 @@ ATVDemod::ATVDemod() :
     m_fltAmpDelta(1.0),
     m_fltAmpLineAverage(0.0f),
     m_intNumberSamplePerTop(0),
+    m_bfoPLL(200/1000000, 100/1000000, 0.01),
+    m_bfoFilter(200.0, 1000000.0, 0.9),
     m_interpolatorDistanceRemain(0.0f),
     m_interpolatorDistance(1.0f),
     m_DSBFilter(0),
@@ -113,14 +115,16 @@ void ATVDemod::configureRF(
         float fltRFBandwidth,
         float fltRFOppBandwidth,
         bool blnFFTFiltering,
-        bool blnDecimatorEnable)
+        bool blnDecimatorEnable,
+        float fltBFOFrequency)
 {
     Message* msgCmd = MsgConfigureRFATVDemod::create(
             enmModulation,
             fltRFBandwidth,
             fltRFOppBandwidth,
             blnFFTFiltering,
-            blnDecimatorEnable);
+            blnDecimatorEnable,
+            fltBFOFrequency);
     objMessageQueue->push(msgCmd);
 }
 
@@ -238,7 +242,7 @@ void ATVDemod::demod(Complex& c)
         int n_out;
         fftfilt::cmplx *filtered;
 
-        n_out = m_DSBFilter->runAsym(c, &filtered, m_objRFRunning.m_enmModulation != ATV_VAML); // all usb except explicitely lsb
+        n_out = m_DSBFilter->runAsym(c, &filtered, m_objRFRunning.m_enmModulation != ATV_LSB); // all usb except explicitely lsb
 
         if (n_out > 0)
         {
@@ -308,7 +312,7 @@ void ATVDemod::demod(Complex& c)
         m_fltBufferQ[0]=fltNormQ;
 
     }
-    else if ((m_objRFRunning.m_enmModulation == ATV_AM) || (m_objRFRunning.m_enmModulation == ATV_VAMU) || (m_objRFRunning.m_enmModulation == ATV_VAML))
+    else if (m_objRFRunning.m_enmModulation == ATV_AM)
     {
         //Amplitude AM
         fltVal = fltNorm;
@@ -329,6 +333,39 @@ void ATVDemod::demod(Complex& c)
         fltVal -= m_fltAmpMin;
         fltVal /=m_fltAmpDelta;
     }
+    else if ((m_objRFRunning.m_enmModulation == ATV_USB) || (m_objRFRunning.m_enmModulation == ATV_LSB))
+    {
+        Real bfoValues[2];
+        float fltFiltered = m_bfoFilter.run(fltI);
+        m_bfoPLL.process(fltFiltered, bfoValues);
+
+        // do the mix
+
+        float mixI = fltI * bfoValues[0] - fltQ * bfoValues[1];
+        float mixQ = fltI * bfoValues[1] + fltQ * bfoValues[0];
+
+        if (m_objRFRunning.m_enmModulation == ATV_USB) {
+            fltVal = (mixI + mixQ);
+        } else {
+            fltVal = (mixI - mixQ);
+        }
+
+        //********** Mini and Maxi Amplitude tracking **********
+
+        if(fltVal<m_fltEffMin)
+        {
+            m_fltEffMin=fltVal;
+        }
+
+        if(fltVal>m_fltEffMax)
+        {
+            m_fltEffMax=fltVal;
+        }
+
+        //Normalisation
+        fltVal -= m_fltAmpMin;
+        fltVal /=m_fltAmpDelta;
+    }
     else
     {
         fltVal = 0.0f;
@@ -560,14 +597,14 @@ bool ATVDemod::handleMessage(const Message& cmd)
         m_objConfig = objCfg.m_objMsgConfig;
 
         qDebug()  << "ATVDemod::handleMessage: MsgConfigureATVDemod:"
-                << " m_fltVoltLevelSynchroBlack" << m_objConfig.m_fltVoltLevelSynchroBlack
+                << " m_fltVoltLevelSynchroBlack:" << m_objConfig.m_fltVoltLevelSynchroBlack
-                << " m_fltVoltLevelSynchroTop" << m_objConfig.m_fltVoltLevelSynchroTop
+                << " m_fltVoltLevelSynchroTop:" << m_objConfig.m_fltVoltLevelSynchroTop
-                << " m_fltFramePerS" << m_objConfig.m_fltFramePerS
+                << " m_fltFramePerS:" << m_objConfig.m_fltFramePerS
-                << " m_fltLineDurationUs" << m_objConfig.m_fltLineDurationUs
+                << " m_fltLineDurationUs:" << m_objConfig.m_fltLineDurationUs
-                << " m_fltRatioOfRowsToDisplay" << m_objConfig.m_fltRatioOfRowsToDisplay
+                << " m_fltRatioOfRowsToDisplay:" << m_objConfig.m_fltRatioOfRowsToDisplay
-                << " m_fltTopDurationUs" << m_objConfig.m_fltTopDurationUs
+                << " m_fltTopDurationUs:" << m_objConfig.m_fltTopDurationUs
-                << " m_blnHSync" << m_objConfig.m_blnHSync
+                << " m_blnHSync:" << m_objConfig.m_blnHSync
-                << " m_blnVSync" << m_objConfig.m_blnVSync;
+                << " m_blnVSync:" << m_objConfig.m_blnVSync;
 
         applySettings();
 
@@ -580,11 +617,12 @@ bool ATVDemod::handleMessage(const Message& cmd)
         m_objRFConfig = objCfg.m_objMsgConfig;
 
         qDebug()  << "ATVDemod::handleMessage: MsgConfigureRFATVDemod:"
-                << " m_enmModulation" << m_objRFConfig.m_enmModulation
+                << " m_enmModulation:" << m_objRFConfig.m_enmModulation
-                << " m_fltRFBandwidth" << m_objRFConfig.m_fltRFBandwidth
+                << " m_fltRFBandwidth:" << m_objRFConfig.m_fltRFBandwidth
-                << " m_fltRFOppBandwidth" << m_objRFConfig.m_fltRFOppBandwidth
+                << " m_fltRFOppBandwidth:" << m_objRFConfig.m_fltRFOppBandwidth
-                << " m_blnFFTFiltering" << m_objRFConfig.m_blnFFTFiltering
+                << " m_blnFFTFiltering:" << m_objRFConfig.m_blnFFTFiltering
-                << " m_blnDecimatorEnable" << m_objRFConfig.m_blndecimatorEnable;
+                << " m_blnDecimatorEnable:" << m_objRFConfig.m_blndecimatorEnable
+                << " m_fltBFOFrequency:" << m_objRFConfig.m_fltBFOFrequency;
 
         applySettings();
 
@@ -677,6 +715,14 @@ void ATVDemod::applySettings()
         m_objSettingsMutex.unlock();
     }
 
+    if ((m_objConfigPrivate.m_intTVSampleRate != m_objRunningPrivate.m_intTVSampleRate)
+        || (m_objRFConfig.m_fltBFOFrequency != m_objRFRunning.m_fltBFOFrequency))
+    {
+        m_bfoPLL.configure(m_objRFConfig.m_fltBFOFrequency / m_objConfigPrivate.m_intTVSampleRate,
+                100.0 / m_objConfigPrivate.m_intTVSampleRate,
+                0.01);
+        m_bfoFilter.setFrequencies(m_objRFConfig.m_fltBFOFrequency, m_objConfigPrivate.m_intTVSampleRate);
+    }
 
     m_objRunning = m_objConfig;
     m_objRFRunning = m_objRFConfig;
@@ -692,3 +738,15 @@ int ATVDemod::getEffectiveSampleRate()
 {
     return m_objRFRunning.m_blndecimatorEnable ? m_objRunningPrivate.m_intTVSampleRate : m_objRunning.m_intSampleRate;
 }
+
+bool ATVDemod::getBFOLocked()
+{
+    if ((m_objRFRunning.m_enmModulation == ATV_USB) || (m_objRFRunning.m_enmModulation == ATV_LSB))
+    {
+        return m_bfoPLL.locked();
+    }
+    else
+    {
+        return false;
+    }
+}

plugins/channelrx/demodatv/atvdemod.h

@@ -31,6 +31,8 @@
 #include "dsp/movingaverage.h"
 #include "dsp/fftfilt.h"
 #include "dsp/agc.h"
+#include "dsp/phaselock.h"
+#include "dsp/recursivefilters.h"
 #include "audio/audiofifo.h"
 #include "util/message.h"
 #include "atvscreen.h"
@@ -46,8 +48,8 @@ public:
 	    ATV_FM1,  //!< Classical frequency modulation with discriminator #1
 	    ATV_FM2,  //!< Classical frequency modulation with discriminator #2
         ATV_AM,   //!< Classical amplitude modulation
-        ATV_VAMU, //!< AM with vestigial lower side band (main signal is in the upper side)
+        ATV_USB,  //!< AM with vestigial lower side band (main signal is in the upper side)
-        ATV_VAML  //!< AM with vestigial upper side band (main signal is in the lower side)
+        ATV_LSB   //!< AM with vestigial upper side band (main signal is in the lower side)
 	};
 
 	struct ATVConfig
@@ -84,6 +86,7 @@ public:
         float         m_fltRFOppBandwidth;
         bool          m_blnFFTFiltering;
         bool          m_blndecimatorEnable;
+        float         m_fltBFOFrequency;
 
         ATVRFConfig() :
             m_intFrequencyOffset(0),
@@ -91,7 +94,8 @@ public:
             m_fltRFBandwidth(0),
             m_fltRFOppBandwidth(0),
             m_blnFFTFiltering(false),
-            m_blndecimatorEnable(false)
+            m_blndecimatorEnable(false),
+            m_fltBFOFrequency(0.0f)
         {
         }
     };
@@ -135,7 +139,8 @@ public:
             float fltRFBandwidth,
             float fltRFOppBandwidth,
             bool blnFFTFiltering,
-            bool blndecimatorEnable);
+            bool blndecimatorEnable,
+            float fltBFOFrequency);
 
 	virtual void feed(const SampleVector::const_iterator& begin, const SampleVector::const_iterator& end, bool po);
 	virtual void start();
@@ -146,6 +151,7 @@ public:
     int getSampleRate();
     int getEffectiveSampleRate();
     double getMagSq() const { return m_objMagSqAverage.average(); } //!< Beware this is scaled to 2^30
+    bool getBFOLocked();
 
 private:
     struct ATVConfigPrivate
@@ -218,14 +224,16 @@ private:
                     float fltRFBandwidth,
                     float fltRFOppBandwidth,
                     bool blnFFTFiltering,
-                    bool blndecimatorEnable)
+                    bool blndecimatorEnable,
+                    int intBFOFrequency)
             {
                 return new MsgConfigureRFATVDemod(
                         enmModulation,
                         fltRFBandwidth,
                         fltRFOppBandwidth,
                         blnFFTFiltering,
-                        blndecimatorEnable);
+                        blndecimatorEnable,
+                        intBFOFrequency);
             }
 
             ATVRFConfig m_objMsgConfig;
@@ -236,7 +244,8 @@ private:
                     float fltRFBandwidth,
                     float fltRFOppBandwidth,
                     bool blnFFTFiltering,
-                    bool blndecimatorEnable) :
+                    bool blndecimatorEnable,
+                    float fltBFOFrequency) :
                 Message()
             {
                 m_objMsgConfig.m_enmModulation = enmModulation;
@@ -244,6 +253,7 @@ private:
                 m_objMsgConfig.m_fltRFOppBandwidth = fltRFOppBandwidth;
                 m_objMsgConfig.m_blnFFTFiltering = blnFFTFiltering;
                 m_objMsgConfig.m_blndecimatorEnable = blndecimatorEnable;
+                m_objMsgConfig.m_fltBFOFrequency = fltBFOFrequency;
             }
     };
 
@@ -286,6 +296,8 @@ private:
     MovingAverage<double> m_objMagSqAverage;
 
     NCO m_nco;
+    SimplePhaseLock m_bfoPLL;
+    SecondOrderRecursiveFilter m_bfoFilter;
 
     // Interpolator group for decimation and/or double sideband RF filtering
     Interpolator m_interpolator;

plugins/channelrx/demodatv/atvdemodgui.cpp

@@ -105,6 +105,7 @@ QByteArray ATVDemodGUI::serialize() const
     s.writeBool(11, ui->halfImage->isChecked());
     s.writeS32(12, ui->rfBW->value());
     s.writeS32(13, ui->rfOppBW->value());
+    s.writeS32(14, ui->bfo->value());
 
     return s.final();
 }
@@ -160,6 +161,8 @@ bool ATVDemodGUI::deserialize(const QByteArray& arrData)
         ui->rfBW->setValue(tmp);
         d.readS32(13, &tmp, 10);
         ui->rfOppBW->setValue(tmp);
+        d.readS32(14, &tmp, 10);
+        ui->bfo->setValue(tmp);
 
         blockApplySettings(false);
         m_objChannelMarker.blockSignals(false);
@@ -336,7 +339,8 @@ void ATVDemodGUI::applyRFSettings()
                 ui->rfBW->value() * 100000.0f,
                 ui->rfOppBW->value() * 100000.0f,
                 ui->rfFiltering->isChecked(),
-                ui->decimatorEnable->isChecked());
+                ui->decimatorEnable->isChecked(),
+                ui->bfo->value() * 10.0f);
     }
 }
 
@@ -349,9 +353,9 @@ void ATVDemodGUI::setChannelMarkerBandwidth()
         m_objChannelMarker.setBandwidth(ui->rfBW->value()*100000);
         m_objChannelMarker.setOppositeBandwidth(ui->rfOppBW->value()*100000);
 
-        if (ui->modulation->currentIndex() == (int) ATVDemod::ATV_VAML) {
+        if (ui->modulation->currentIndex() == (int) ATVDemod::ATV_LSB) {
             m_objChannelMarker.setSidebands(ChannelMarker::vlsb);
-        } else if (ui->modulation->currentIndex() == (int) ATVDemod::ATV_VAMU) {
+        } else if (ui->modulation->currentIndex() == (int) ATVDemod::ATV_USB) {
             m_objChannelMarker.setSidebands(ChannelMarker::vusb);
         } else {
             m_objChannelMarker.setSidebands(ChannelMarker::vusb);
@@ -413,6 +417,12 @@ void ATVDemodGUI::tick()
             m_objMagSqAverage.feed(m_objATVDemod->getMagSq());
             double magSqDB = CalcDb::dbPower(m_objMagSqAverage.average() / (1<<30));
             ui->channePowerText->setText(tr("%1 dB").arg(magSqDB, 0, 'f', 1));
+
+            if (m_objATVDemod->getBFOLocked()) {
+                ui->bfoLockedLabel->setStyleSheet("QLabel { background-color : green; }");
+            } else {
+                ui->bfoLockedLabel->setStyleSheet("QLabel { background:rgb(79,79,79); }");
+            }
         }
 
         m_intTickCount = 0;
@@ -525,3 +535,9 @@ void ATVDemodGUI::on_deltaFrequencyMinus_toggled(bool minus)
     }
 }
 
+void ATVDemodGUI::on_bfo_valueChanged(int value)
+{
+    ui->bfoText->setText(QString("%1").arg(value * 10.0, 0, 'f', 0));
+    applyRFSettings();
+}
+

plugins/channelrx/demodatv/atvdemodgui.h

@@ -79,6 +79,7 @@ private slots:
     void on_decimatorEnable_toggled(bool checked);
     void on_deltaFrequency_changed(quint64 value);
     void on_deltaFrequencyMinus_toggled(bool minus);
+    void on_bfo_valueChanged(int value);
 
 private:
 	Ui::ATVDemodGUI* ui;

plugins/channelrx/demodatv/atvdemodgui.ui

@@ -40,7 +40,7 @@
      <x>10</x>
      <y>10</y>
      <width>501</width>
-     <height>71</height>
+     <height>81</height>
     </rect>
    </property>
    <property name="windowTitle">
@@ -52,23 +52,6 @@
     </property>
     <item>
      <layout class="QHBoxLayout" name="rfSettings1Layout">
-      <item>
-       <widget class="ButtonSwitch" name="decimatorEnable">
-        <property name="toolTip">
-         <string>Toggle decimator on/off</string>
-        </property>
-        <property name="text">
-         <string/>
-        </property>
-        <property name="icon">
-         <iconset resource="../../../sdrbase/resources/res.qrc">
-          <normaloff>:/arrow_down.png</normaloff>:/arrow_down.png</iconset>
-        </property>
-        <property name="checkable">
-         <bool>true</bool>
-        </property>
-       </widget>
-      </item>
       <item>
        <layout class="QHBoxLayout" name="deltaFrequencyLayout">
         <item>
@@ -124,6 +107,30 @@
         </item>
        </layout>
       </item>
+      <item>
+       <widget class="Line" name="line_3">
+        <property name="orientation">
+         <enum>Qt::Vertical</enum>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <widget class="ButtonSwitch" name="decimatorEnable">
+        <property name="toolTip">
+         <string>Toggle decimator on/off</string>
+        </property>
+        <property name="text">
+         <string/>
+        </property>
+        <property name="icon">
+         <iconset resource="../../../sdrbase/resources/res.qrc">
+          <normaloff>:/arrow_down.png</normaloff>:/arrow_down.png</iconset>
+        </property>
+        <property name="checkable">
+         <bool>true</bool>
+        </property>
+       </widget>
+      </item>
       <item>
        <widget class="QLabel" name="channelSampleRateText">
         <property name="minimumSize">
@@ -144,35 +151,77 @@
        </widget>
       </item>
       <item>
-       <widget class="QComboBox" name="modulation">
+       <widget class="Line" name="line">
+        <property name="orientation">
+         <enum>Qt::Vertical</enum>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <widget class="QLabel" name="bfoLockedLabel">
+        <property name="maximumSize">
+         <size>
+          <width>22</width>
+          <height>22</height>
+         </size>
+        </property>
+        <property name="text">
+         <string/>
+        </property>
+        <property name="pixmap">
+         <pixmap resource="../../../sdrbase/resources/res.qrc">:/carrier.png</pixmap>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <widget class="QDial" name="bfo">
+        <property name="maximumSize">
+         <size>
+          <width>22</width>
+          <height>22</height>
+         </size>
+        </property>
         <property name="toolTip">
-         <string>Modulation type</string>
+         <string>BFO frequency adjust</string>
         </property>
-        <item>
+        <property name="minimum">
-         <property name="text">
+         <number>-500</number>
-          <string>FM 1</string>
         </property>
+        <property name="maximum">
+         <number>500</number>
+        </property>
+        <property name="pageStep">
+         <number>1</number>
+        </property>
+        <property name="value">
+         <number>0</number>
+        </property>
+       </widget>
       </item>
       <item>
-         <property name="text">
+       <widget class="QLabel" name="bfoText">
-          <string>FM 2</string>
+        <property name="minimumSize">
+         <size>
+          <width>40</width>
+          <height>0</height>
+         </size>
         </property>
+        <property name="toolTip">
+         <string>BFO frequency (Hz)</string>
+        </property>
+        <property name="text">
+         <string>0</string>
+        </property>
+        <property name="alignment">
+         <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
+        </property>
+       </widget>
       </item>
       <item>
-         <property name="text">
+       <widget class="Line" name="line_2">
-          <string>AM</string>
+        <property name="orientation">
+         <enum>Qt::Vertical</enum>
         </property>
-        </item>
-        <item>
-         <property name="text">
-          <string>VAMU</string>
-         </property>
-        </item>
-        <item>
-         <property name="text">
-          <string>VAML</string>
-         </property>
-        </item>
        </widget>
       </item>
       <item>
@@ -211,6 +260,38 @@
     </item>
     <item>
      <layout class="QHBoxLayout" name="rfSettings2Layout">
+      <item>
+       <widget class="QComboBox" name="modulation">
+        <property name="toolTip">
+         <string>Modulation type</string>
+        </property>
+        <item>
+         <property name="text">
+          <string>FM 1</string>
+         </property>
+        </item>
+        <item>
+         <property name="text">
+          <string>FM 2</string>
+         </property>
+        </item>
+        <item>
+         <property name="text">
+          <string>AM</string>
+         </property>
+        </item>
+        <item>
+         <property name="text">
+          <string>USB</string>
+         </property>
+        </item>
+        <item>
+         <property name="text">
+          <string>LSB</string>
+         </property>
+        </item>
+       </widget>
+      </item>
       <item>
        <widget class="ButtonSwitch" name="rfFiltering">
         <property name="toolTip">

sdrbase/dsp/phaselock.h

@@ -112,6 +112,24 @@ private:
     std::vector<PpsEvent> m_pps_events;
 };
 
+class SimplePhaseLock : public PhaseLock
+{
+public:
+    SimplePhaseLock(Real freq, Real bandwidth, Real minsignal) :
+        PhaseLock(freq, bandwidth, minsignal)
+    {}
+
+    virtual ~SimplePhaseLock()
+    {}
+
+protected:
+    virtual void processPhase(Real *samples_out) const
+    {
+        samples_out[0] = m_psin; // f Pilot
+        samples_out[1] = m_pcos; // f Pilot
+    }
+};
+
 class StereoPhaseLock : public PhaseLock
 {
 public:

sdrbase/dsp/recursivefilters.cpp

@@ -0,0 +1,69 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2017 Edouard Griffiths, F4EXB                                   //
+//                                                                               //
+// This program is free software; you can redistribute it and/or modify          //
+// it under the terms of the GNU General Public License as published by          //
+// the Free Software Foundation as version 3 of the License, or                  //
+//                                                                               //
+// This program is distributed in the hope that it will be useful,               //
+// but WITHOUT ANY WARRANTY; without even the implied warranty of                //
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                  //
+// GNU General Public License V3 for more details.                               //
+//                                                                               //
+// You should have received a copy of the GNU General Public License             //
+// along with this program. If not, see <http://www.gnu.org/licenses/>.          //
+///////////////////////////////////////////////////////////////////////////////////
+
+#include <cmath>
+#include "recursivefilters.h"
+
+SecondOrderRecursiveFilter::SecondOrderRecursiveFilter(float samplingFrequency, float centerFrequency, float r) :
+        m_r(r),
+        m_frequencyRatio(centerFrequency/samplingFrequency)
+{
+    init();
+}
+
+SecondOrderRecursiveFilter::~SecondOrderRecursiveFilter()
+{}
+
+void SecondOrderRecursiveFilter::setFrequencies(float samplingFrequency, float centerFrequency)
+{
+    m_frequencyRatio = centerFrequency / samplingFrequency;
+    init();
+}
+
+void SecondOrderRecursiveFilter::setR(float r)
+{
+    m_r = r;
+    init();
+}
+
+short SecondOrderRecursiveFilter::run(short sample)
+{
+    m_v[0] = ((1.0f - m_r) * (float) sample) + (2.0f * m_r * cos(2.0*M_PI*m_frequencyRatio) * m_v[1]) - (m_r * m_r * m_v[2]);
+    float y = m_v[0] - m_v[2];
+    m_v[2] = m_v[1];
+    m_v[1] = m_v[0];
+
+    return (short) y;
+}
+
+float SecondOrderRecursiveFilter::run(float sample)
+{
+    m_v[0] = ((1.0f - m_r) * sample) + (2.0f * m_r * cos(2.0*M_PI*m_frequencyRatio) * m_v[1]) - (m_r * m_r * m_v[2]);
+    float y = m_v[0] - m_v[2];
+    m_v[2] = m_v[1];
+    m_v[1] = m_v[0];
+
+    return y;
+}
+
+void SecondOrderRecursiveFilter::init()
+{
+    for (int i = 0; i < 3; i++)
+    {
+        m_v[i] = 0.0f;
+    }
+}
+

sdrbase/dsp/recursivefilters.h

@@ -0,0 +1,45 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2017 Edouard Griffiths, F4EXB                                   //
+//                                                                               //
+// This program is free software; you can redistribute it and/or modify          //
+// it under the terms of the GNU General Public License as published by          //
+// the Free Software Foundation as version 3 of the License, or                  //
+//                                                                               //
+// This program is distributed in the hope that it will be useful,               //
+// but WITHOUT ANY WARRANTY; without even the implied warranty of                //
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                  //
+// GNU General Public License V3 for more details.                               //
+//                                                                               //
+// You should have received a copy of the GNU General Public License             //
+// along with this program. If not, see <http://www.gnu.org/licenses/>.          //
+///////////////////////////////////////////////////////////////////////////////////
+
+#ifndef SDRBASE_DSP_RECURSIVEFILTERS_H_
+#define SDRBASE_DSP_RECURSIVEFILTERS_H_
+
+/**
+ * \Brief: This is a second order bandpass filter using recursive method. r is in range ]0..1[ the higher the steeper the filter.
+ * inspired by:http://www.ece.umd.edu/~tretter/commlab/c6713slides/FSKSlides.pdf
+ */
+class SecondOrderRecursiveFilter
+{
+public:
+    SecondOrderRecursiveFilter(float samplingFrequency, float centerFrequency, float r);
+    ~SecondOrderRecursiveFilter();
+
+    void setFrequencies(float samplingFrequency, float centerFrequency);
+    void setR(float r);
+    short run(short sample);
+    float run(float sample);
+
+private:
+    void init();
+
+    float m_r;
+    float m_frequencyRatio;
+    float m_v[3];
+};
+
+
+
+#endif /* SDRBASE_DSP_RECURSIVEFILTERS_H_ */